WO2019096492A1

WO2019096492A1 - High head type optical display device

Info

Publication number: WO2019096492A1
Application number: PCT/EP2018/077329
Authority: WO
Inventors: Yanning Zhao; Elie Abi Chaaya; Patrick Nebout; Jean-Christophe JOLY-VUILLEMIN; Giang-Nam NGUYEN
Original assignee: Visteon Global Technologies, Inc.
Priority date: 2017-10-02
Filing date: 2018-10-08
Publication date: 2019-05-23

Abstract

The present invention relates to an optical display device (1) of the head-up type comprising: a windshield (2) or a combiner, an image generation unit (3) for generating at least one source image, a relay optics (4) for forming from said at least one source image at least one virtual image (5) projected at a given distance via said windshield (2) or said combiner, the relay optics (4) comprising at least one optical component (4'), characterized in that: the optical display device (1) comprises a holographic optical element (6) arranged or integrated on or in said at least one optical component (4') of the relay optics (4), the windshield (2) or the combiner, and the holographic optical element (6) comprises a reflection hologram.

Description

DESCRIPTION

High head type optical display device

The present invention relates to the field of optical display devices of the head-up type, in particular for motor vehicles.

Many embodiments of an optical display device 1 of the head-up type, an exemplary configuration of which is illustrated in FIG. 1, are already known. This optical display device 1 of the head-up type has the function of allowing the superposition of a real image (not shown) such as a road, seen in the field of view of a conductor 7 through a windshield 2, and a virtual image 5, which is projected at a given distance at the level of the windshield 2 of a vehicle. The virtual image 5 is obtained from an image generation unit 3 generating a source image that is projected at a given distance via a relay optics 4, comprising a combination of optical components, for example, an intermediate screen 4' and mirrors 4", 4"'.

Lasers are particularly suitable for forming a light source for producing vivid images with a wide range of colors and contrast due to their high optical efficiency. The publication US 2012/0224062 A1 advantageously describes the use of lasers as an image generation unit, in a head-up type optical display device.

Furthermore, it is preferable that, firstly, the projected virtual image extends into the driver's field of view and, secondly, that two virtual images can also be displayed in two distinct planes, to maximize the augmented reality effect. However, the size of the virtual image, as well as the number of virtual images, are limited by the dimensions of the relay optics, which is necessary to project the virtual image or the virtual images at a given distance. Indeed, the volume of the relay optics must be able to fit inside a slot provided below the dashboard, which is limited in terms of volume. However, in general, the more a virtual image of quality is sought, the more the number of optical components increases in the relay optics and consequently the volume of the optical display device increases.

Publication CN 103513420 A discloses a method of designing a relay optics comprising a transparent type holographic optical element for a head-up display device mounted in a vehicle. This holographic optical element is used to replace a traditional refractive optical element, in order to reduce the size, the weight of the device, reduce production costs, simplify the structure, reduce assembly difficulties, and allow installation in a small space. More particularly, the holographic optical element comprises a transmission hologram for reproducing the optical properties of a lens. However, in this configuration, the optical element is part of the relay optics, therefore, even if the thickness of the holographic optical element is negligible, the volume of the head-up display device is still limited by the optical paths before and after the holographic optical element which are inside the relay optics

The object of the present invention is to propose an improved head-up type optical display device, which is small and easily integrates into a limited space, located, for example, under the dashboard of a vehicle.

For this purpose, the invention relates to a head-up type optical display device comprising:

- a windshield or a combiner,

- an image generation unit for generating at least one source image,

- a relay optics for forming from said at least one source image at least one projected virtual image at a given distance via said windshield or said combiner, the relay optics comprising at least one optical component,

characterized in that:

the optical display device comprises a holographic optical element arranged or integrated on or in said at least one optical component of the relay optics, the windshield or the combiner, and the holographic optical element comprises a reflection hologram.

The invention will be better understood thanks to the following description, which relates to several preferred embodiments, given by way of non-limiting examples, and explained with reference to the appended diagrammatic drawings, in which:

FIG. 1 is a view of a head-up optical display device known from the prior art,

FIG. 2 is a view of a recording device of a reflective holographic optical element for an optical display device according to the invention,

FIG. 3 is a view of a transmission spectrum of the reflective holographic optical element as a function of the wavelength,

FIG. 4 is a view of a head-up optical display device according to the invention,

FIG 5 is a view of another head-up optical display device according to the invention, and

FIG. 6 shows a comparison of the angular and wavelength selectivity between transmission and reflection holograms.

As illustrated in FIG. 4, the head-type optical display device 1 comprises:

- a windshield 2 or a combiner (not shown),

- an image generation unit 3 for generating at least one source image (not represented), - relay optics 4 for forming from said at least one source image at least one projected virtual image at a given distance through said windshield 2 or said combiner, the relay optics 4 comprising at least one optical component 4'.

According to the invention the optical display device 1 is characterized in that it comprises a reflective holographic optical element 6 arranged or integrated on or in said at least one optical component 4' of the relay optics 4, the windshield 2 or the combiner, and in that the holographic optical element 6 comprises a reflection hologram.

Said at least one virtual image 5 is preferably projected at a given distance via said windshield 2 or said combiner, for example between 8 meters and 15 meters.

A holographic optical element 6, also known by the abbreviation HOE, is an optical element including at least one hologram.

A hologram of reflection is a hologram that is recorded by means of two interfering laser beams 8, 9 that are incident at opposite sides 10a, 10b of a recording medium 10 (FIG. 2). A first beam 8, called a reference beam, is sent directly to the recording medium 10 and a second beam 9 is sent to the object to be recorded, for example a relay optics 4, and is called an object beam 9' at the side of the object. Advantageously, such a reflection hologram, when it is re-illuminated by the first beam 8, referred to as the reference beam, reflects this reference beam and reconstructs the object beam 9'.

This advantageous configuration according to the invention makes it possible to replace optical components usually present at the level of the relay optics 4, such as reflective optical components, for example mirrors, by a holographic optical element 6 comprising a reflection hologram. In the prior art and as illustrated in FIG. 1, these reflective optical components are bulky in order to increase the quality of the virtual image 5. As a result, the replacement of such reflective optical components of the prior art by a holographic optical element 6, makes it possible to reduce the size and the weight of the optical display device 1 while preserving the quality of the virtual image 5. The holographic optical element 6 makes it possible to diffract the light waves coming from the image generation unit 3 using a particular material profile to form new light waves. On the contrary, conventional optical components, such as lenses, refract or reflect these light waves. The holographic optical element 6 can advantageously reproduce the optical functions of standard lenses, or standard arrays, or standard mirrors, but has the advantage of being lighter and less bulky than these standard optical components.

The holographic optical element 6 may comprise a recording medium 6' in film form, in which the reflection hologram is recorded, and disposed or integrated on or in said at least one optical component 4' of the relay optics 4, the windshield 2 or the combiner (Figure 4).

The use of a recording medium 6' in film form forms a support adapted to the recording of the hologram and contributes additionally to the miniaturization of the optical display device 1, while facilitating the integration of the holographic optical element 6. Moreover, in the film form, the recording medium 6' scan then be integrated over large areas, preferably a few hundred square centimeters, for example at the level of the windshield 2.

According to a preferred configuration, the holographic optical element 6 comprises a recording medium 6' in film form, in which the reflection hologram is recorded, and disposed or integrated on or in said windshield 2 or the combiner, and the relay optics 4 may comprise a single optical component 4' which consists of an intermediate screen disposed between the image generation unit 3 and the windshield 2 or the combiner.

Advantageously, the holographic optical element 6 replaces in this case the mirrors 4", 4"' of the relay optics 4 according to the prior art which is illustrated in FIG. 1. According to this construction of the optical display device 1 according to the invention, the size of the optical display device l ean be considerably reduced. Indeed, only the image generation unit 3 and a single optical component 4', preferentially in the form of an intermediate screen, are necessary, additional mirrors may be used to further improve image quality, but are no longer necessary. As a result, the intended location below the dashboard can be considerably limited in terms of volume, since it can be reduced to the volume of the image generation unit 3 and the intermediate screen. Indeed, in this preferred configuration, the optical holographic element 6 is not located in the space below the dashboard and therefore does not contribute to the size of this space.

The recording medium 6' in film form may comprise a material selected from the group consisting of photopolymerized materials, silver halide, dichromated gelatin, photoresist, photorefractive glass, a photographic emulsion and thermoplastic materials.

This type of recording medium 6' is particularly suitable for recording holograms.

Preferably, the recording medium 6' in film form of photopolymerized material may have a thickness of between 10 and 80 microns.

Advantageously, the recording medium 6' in film form has a sufficiently thin thickness relative to the thickness of the windshield 2 or the combiner or at least one optical component 4' of the relay optics 4 facilitating its integration. The thickness of a windshield 2 is generally between 4 and 6 millimeters.

The recording medium 6' in film form of photopolymerized material may comprise a photopolymer layer sensitive to light, and where appropriate may be associated with a substrate layer.

The substrate layer may be of cellulose.

The windshield 2 or the combiner may be laminated and the holographic optical element 6 may be integrated into the laminated glass of the windshield 2 or the combiner, thanks to the high transparency of the photopolymer material, as illustrated in FIG. 3. Advantageously, in this way the holographic optical element 6 can be integrated in the windshield 2 or the combiner during the manufacture of the windshield 2 or the combiner. This results in an easy assembly of the optical display device 1.

The holographic optical element 6 can be laminated in the windshield 2 or can be integrated between two sheets of glass (not shown), more particularly, the recording medium 6' in film form can be laminated in the windshield 2 or can be integrated between the two glass sheets of the windshield 2.

For example, the holographic optical element 6 integrated at the level of the windshield 2 may have an area of 10 centimeters x 20 centimeters.

This example is not limiting and the surface of the holographic optical element 6 may be smaller or larger.

Alternatively and in a configuration not illustrated, the holographic optical element 6 may be arranged at the relay optics 4, for example, integrated with a mirror or a lens, as illustrated in FIG

5.

The image generation unit 3 may comprise a red-green-blue laser emitting around three wavelengths, a first wavelength li, a second wavelength l₂, and a third wavelength h .

The use of such an image generation unit 3 makes it possible to produce vivid images with a wide range of colors and contrast.

The first wavelength li may be centered around 470 nanometers, the second wavelength l₂ may be centered around 527 nanometers, and the third wavelength h may be centered around 663 nanometers.

In this case, the holographic optical element 6 may be an element selectively reflecting the three wavelengths li, l₂, K3 emitted by said laser of the image generation unit 3 according to a transmission rate less than or equal to 25% (meaning reflection rate higher than or equal to 75%) and transmitting the other wavelengths of the spectrum of visible light between 440 nanometers and 680 nanometers with a transmission rate greater than or equal to 75%.

This transmission rate, greater than or equal to 75%, makes it possible to satisfy the transparency standard of the windshield 2. Moreover, the selective reflection of the three wavelengths li, l₂, l3 by the holographic optical element 6 makes it possible to visualize virtual colored images for the driver 7.

A holographic optical element 6 having the above characteristics may be formed in a photopolymerizable film marketed by COVESTRO under the name Bayfol HX200, registered trademark, described below. The transmission spectrum of the holographic optical element 6 recorded in such a film is shown in FIG. 3. This transmission spectrum illustrates that the holographic optical element 6 obtained on the one hand reflects the first wavelength li centered around 470 nanometers, the second wavelength l₂ centered around 527 nanometers, and the third wavelength h centered around 663 nanometers and, on the other hand, transmits the other wavelengths of the spectrum of the visible light between 400 nanometers and 700 nanometers.

The properties of the holographic optical element 6 can be stable for temperatures between -40 degrees Celsius and 150 degrees Celsius.

The term "stable" means that the holographic optical element 6 is not degraded by thermal energy in this temperature range.

Indeed, during the method of manufacturing a windshield 2, the temperature can reach up to substantially 140 degrees Celsius for a few tens of minutes. Advantageously, such a stable holographic optical element 6 is thus not degraded under the effect of heat during the manufacture of the windshield 2.

The holographic optical element 6 of the optical display device 1 according to the invention can be manufactured by means of a recording device illustrated in FIG. 2 in the recording medium 6' in film form. To do this, the optical function of the relay optics 4 of the optical display device 1 of the prior art illustrated in FIG. 1, for example the optical function of a mirror or of several mirrors 4", 4' of the relay optics 4 of the prior art, is recorded in the recording medium 6' in film form, preferably photopolymerizable. The recording of the holographic optical element 6 is performed by interfering two coherent light beams 8, 9, preferably two laser beams, at the recording medium 6' in film form. A first beam 8 is sent directly to the recording medium 6' in film form. The second beam 9 is sent to the relay optics 4, the optical function of which is to be recorded, which diffuses the light towards the recording medium 6' in film form. An interference pattern is formed, which includes information about the amplitude and phase of the wave of the relay optics 4.

To facilitate the recording of the hologram and the manipulation of the recording medium, the recording medium 6' can be associated with a substrate 6", which is preferably transparent (FIG. 2). Preferably, the recording medium 6' is laminated on the substrate 6". Advantageously, the substrate 6" allows to facilitate the recording operation by keeping the recording medium 6' in film form. The recording medium 6' in film form can be removed from the substrate 6" after the hologram is recorded to be laminated at the windshield 2. The substrate 6" may be a flat or curved glass.

This assembly of recording medium 6' - substrate 6" forms a recording means 10.

The recording medium 6' can also be associated with a protective layer (not shown). This protective layer may cover the recording medium 6'. It allows to protect the recording medium 6' and can be removed before the recording of the hologram. The protective layer may be a polyethylene film. An exemplary recording medium 6' with a protective layer may consist of an assembly of a protective film layer comprising a cellulose layer, a light-sensitive photopolymer layer, and a polyethylene layer; marketed by COVESTRO under the name Bayfol HX200, registered trademark.

Advantageously, this recording medium 6' is well suited for the recording of volume holograms, such as reflection holograms, which is the subject of the present invention.

A volume hologram is a hologram whose recording medium 6', here in film form, has a thickness which is greater relative to the wavelength used to record the hologram. In this case, the diffraction of the light coming from the hologram is only possible by Bragg diffraction, that is to say, only when the light has the right wavelength and the wave has the right shape (wavefront profile, beam direction). Such volume holograms are also referred to as thick holograms or Bragg holograms.

Of course, the holographic optical element 6 can be recorded in different configurations by changing for example the wavelengths of the light beams 8, 9 used and/or their polarization of the recording device. Therefore, several images can be separated using the holographic optical element 6 and appear at different distances, either by wavelength division multiplexing or polarization multiplexing.

In general, by virtue of the use of the holographic optical element 6 according to the invention, it is possible to improve the quality of the virtual image 5, to improve the brightness, the resolution, the contrast, and to correct the distortions.

FIG. 5 shows another embodiment of an optical display device 1 of the head-up type according the present invention. Compared to the embodiment of the optical display device illustrated in FIG. 4, the holographic optical element 6 is not arranged on or in the windshield but on a flat or curved surface 4" of the relay optics 4. In particular, the reflective holographic optical element 6 may be used as a mirror. This way the package size may be reduced compared to the embodiment of FIG. 1 but still biggerthan the embodiment of FIG. 4 in which the holographic optical element 6 is integrated in the windshield 2 or a combiner. In particular, the holographic optical element 6 is a reflective holographic optical element.

FIG. 6 shows a comparison of the angular and wavelength selectivity between transmission and reflection holograms. Transmission holograms have very narrow angular selectivity, which means that the incident angle cannot vary. Thus, when using a transmission hologram, the driver can only see the virtual image when viewing from a specific position. A reflection hologram on the other hand has a much wider angular selectivity, providing a wider eye box which is necessary for automotive applications using an optical display device of the head-up type. On the other hand, reflection hologram has a narrower wavelength selectivity which prevents negative effects of the ambient light such as sunlight to the driver. For transmission hologram, a big part of the visible spectrum can pass through and diffract, leading to stray light as well as color dispersion, which interfere with the image from the display. Therefore, a transmission hologram can only be used as a lens inside the optical display device and should not be exposed to ambient light, while a reflection hologram can be integrated on windshield or combiner and therefore further reduces the size of the optical display device.

Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications are possible, especially from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims

1. An optical display device (1) of the head-up type comprising:

a windshield (2) or a combiner,

an image generation unit (3) for generating at least one source image,

a relay optics (4) for forming from said at least one source image at least one virtual image (5) projected at a given distance via said windshield (2) or said combiner, the relay optics (4) comprising at least one optical component (4'),

characterized in that:

the optical display device (1) comprises a holographic optical element (6) arranged or integrated on or in said at least one optical component (4') of the relay optics (4), the windshield ( 2) or the combiner, and

the holographic optical element (6) comprises a reflection hologram.

2. Device according to Claim 1, characterized in that the holographic optical element (6) comprises a recording medium (6') in film form, in which the reflection hologram is recorded, and arranged or integrated on or in said at least one optical component (4') of the relay optics (4), the windshield (2) or the combiner.

3. Device according to Claim 1, characterized in that the holographic optical element (6) comprises a recording medium (6') in film form, in which the reflection hologram is recorded, and arranged or integrated on or in said windshield (2) or the combiner and the relay optics (4) comprise a single optical component (4') which consists of an intermediate screen arranged between the image generation unit (3) and the windshield (2) or the combiner.

4. Device according to any one of claims 1 to 3, characterized in that the recording medium (6') in film form comprises a material selected from the group consisting of photopolymerized materials, silver halide, dichromated gelatin, photoresist, photorefractive glass, photographic emulsion and thermoplastic materials.

5. Device according to Claim 4, characterized in that the recording medium (6') in film form of photopolymerized material has a thickness of between 10 and 80 microns.

6. Device according to claim 5, characterized in that the recording medium (6') in film form of photopolymerized material may comprise a photopolymer layer sensitive to light and where appropriate is associated with a substrate layer.

7. Device according to claim 6, characterized in that the substrate layer is made of cellulose.

8. Device according to one of Claims 1 to 7, characterized in that the windscreen (2) or the combiner is made of laminated glass and the holographic optical element (6) is integrated in the laminated glass of the windscreen (2) or combiner.

9. Device according to any one of claims 1 to 8, characterized in that the image generation unit (3) comprises a red-green-blue laser emitting around three wavelengths, a first wavelength li, a second wavelength l₂, a third wavelength h.

10. Device according to claim 9, characterized in that the first wavelength li is centered around 470 nanometers, the second wavelength l₂ is centered around 527 nanometers, the third wavelength h is centered around 663 nanometers.

11. Device according to any one of claims 9 to 10, characterized in that the holographic optical element (6) is a selectively reflecting element the three wavelengths li, l₂, l3 emitted by said laser of the generating unit of images (3) with a transmission rate of less than or equal to 25% (equivalent to a reflection rate of higher than or equal to 75%) and transmitting the other wavelengths of the visible light spectrum between 400 nanometers and 700 nanometers with a transmission rate greater than or equal to 75%.

12. Device according to any one of claims 1 to 11, characterized in that the properties of the holographic optical element (6) are stable for temperatures between -40 degrees Celsius and 150 degrees Celsius.